If it's to hard to understand the gold-silver comparison, I don't think this person would understand btc and buy them. The part that more cryptocurrencies exist just like metals is probably the easiest part to understand.

I may be wrong but it looks like in the long run, the only advantage of LTC for most people would be that transactions are faster than BTC.

is there any way that BTC transactions could be made faster in order to compete with LTC for buying stuff?

That's the most irelevant difference between LTC/BTC. LTC will provide diversification and that's why LTC might be even 1:1 on BTC. When some big players move at the only crypto it generates vola and panic/greed. Too much vola makes a currency useless.

On a multi crypto enviroment panic sellers can move to the alternative crypto(s) and the overall market vola on crypto stays lower. But don't worry, one 50% less volatile bitcoin at 30% market cap is definitively more worth than 1 BTC of todays 95% cap.

BTC is quite stable now at the 100$ value so for many investors it is not that interesting anymore. LTC is still in it's early days, the network hashrate and difficulty is at it's all time high and more (underground) merchants are starting to accepts Litecoins. So for an investor/newbie it will be far more interesting to invest in LTC then in BTC.

I expect a lot of BTC owners to sell some BTC for LTC, thus decreasing value of BTC and increasing value of LTC.But hey, I could be wrong.

Also, the CEO of MtGox has said on Twitter that LTC and NMC will be added. Now they are just being vague and saying "other crypto currencies" but I think that there is a good chance that LTC and NMC get added.